The present invention relates to a friction stir welding method suitable for use in a joining of members of various materials, including, for example, an aluminum alloy member, etc.
A friction stir welding method is a method in which by rotating a round-shaped rod (a rotary body) inserted in a joining region between two members (e.g., but not limiting, two metal bodies, such as two Al bodies), and further by moving the rotary body along a joining line, the two bodies at the joining region are heated, and material thereof softened and plastically fluidized and thus the two bodies are solid-phase joined, e.g., are welded together at the joining region.
Conventionally, the rotary body comprises a small diameter portion which is inserted in the joining region and a large diameter portion which is positioned outside the joining region. The small diameter portion and the large diameter portion are positioned on the same axis. A side of the large diameter portion is rotated, whereby both the large and small diameter portions are rotated. A boundary portion between the small diameter portion and the large diameter portion can be inserted a little into the joining region. A joining according to the friction stir welding method can be applied to an abutting portion and an overlapping portion.
The above-stated prior technique is disclosed, for example, in Japanese patent announcement laid-open publication No. Hei 7-505090 (EP 0615480 Bi); Dawes, xe2x80x9cAn Introduction to Friction Stir Welding and Its Developmentxe2x80x9d, in Welding and Metal Fabrication (January 1995), pages 13, 14 and 16; and by U.S. patent application Ser. No. 08/820,231, filed Mar. 18, 1997, the contents of which are incorporated herein by reference in their entirety.
This prior technique is also described in the article by T. Shinoda and Y. Kondoh, xe2x80x9c324 Butt Welding of Plate Using Friction Stir Welding; Method Study of Friction Stir Weldingxe2x80x9d, Welding Associate Japan Lecture Meeting Outline, No. 56 (April 1995), pages 208 and 209. This article discloses a rotary body (rotary tool) made of stainless steel, members to be welded (joined) made of pure aluminum (A1100), and the members to be welded having a plate thickness of 6 mm. The rotary body has a large diameter portion with a diameter of 20 mm, and a small diameter portion (cylindrical) with a diameter of 6 mm and a length (axially) of 5 mm. In operation, the rotary body rotates at 1000-2500 rpm, and moves along the two members to be welded at a speed of 1.0-8.0 mm/s.
In the article described in the foregoing paragraph, the members to be joined are made of aluminum. Alloys of aluminum are also suitable for welding by friction stir welding; other metals studied for welding by friction stir welding include copper, titanium and stainless steel. EP 0615480 B1, referred to previously herein, discloses friction stir welding of plastic (e.g., thermoplastic) materials. All of these materials can be welded by the process of the present invention.
According to various experiments of the friction stir welding method, a part of an upper face of a joining region of two members is machined as chips, by a rotation of the large diameter portion of the rotary body, and a dent is caused in the upper face of the joining region. At both sides of the dent, a thickened part is caused according to plastic deformation of the members.
It is easy to delete the thickened part; however, correcting for the dent needs a putty working, etc., and as a result a high manufacturing cost is caused.
Further, in a case where before the joining working a gap exists between end faces of the abutting faces of the two members, a default such as a dent, etc., is generated at the joining region. As a result, a lowering in strength is caused, and particularly in a large-scale construction it invites a problem. The larger the members, the more a management in the above-stated gap becomes difficult (i.e., the more the gap occurs); accordingly, the dent becomes large, and, moreover, a default is generated easily.
In a case where the joining region is covered by another member, for example, the existence of the dent is not as much a problem, and there is no problem except for the strength problem (which, of course, can be a serious problem itself). However, in a side face, etc., of a car body of cars (e.g., railroad cars), it is necessary to remove the dent from a viewpoint of an outward appearance. Further, even in a case where the dent is not visible, the dent becomes a problem from an aspect of the performance (e.g., strength of the weld).
An object of the present invention is to prevent generation of a dent in a joining region when joining two members (e.g., but not limited to, two metal members, such as of aluminum alloy) by a friction stir welding method.
Another object of the present invention is to provide members, to be joined by friction stir welding, which avoid a dent in the joining region between the joined members.
Still another object of the present invention is to provide a friction stir welding method, and product manufactured thereby, whereby a dent can be avoided in the joining region between joined members, where the members joined are abutting each other before being joined or even where there is a small gap between the members before they are joined (but the members are adjacent each other).
The above-stated objects can be attained by a provision where at least one of the members to be joined has a thickened part, in cross section, at the joining region thereof with another member, the thickened part protruding toward the rotary body used to perform the friction stir welding. The rotary body has large and small diameter portions, e.g., made of a material or materials harder than the material of the members to be welded, the small diameter portion first being inserted in the joining region of the members to be joined, during the joining. The members to be joined are positioned adjacent each other, with the thickened part of one member being positioned adjacent the other member to be joined thereto by welding. Where both members have thickened parts, the thickened parts can be positioned adjacent each other in the joining (joint-forming) region, or only one thickened part need be positioned in the joint-forming region. The rotary body is then caused to enter between the two members, in the joining region, with the small diameter portion of the rotary body being inserted into the joint-forming region of the two members and the large diameter portion of the rotary body extending into the thickened part (but not below the thickened part). The rotary body is then moved along the members to be welded, in the joining region, with the rotary body inserted as described in the previous sentence to perform the friction stir welding. Due to provision of the thickened part, at the joint-forming region, a dent (depressed region) at the weld region, in the joined members, can be avoided. By positioning the rotary body such that the large-diameter portion thereof is inserted into the thickened part (overlaps with the thickened part), an excellent weld is achieved, while avoiding a dent in the welded joint. Advantageously, the large-diameter portion of the rotary body does not extend below the protruding portion of the thickened part, while moving the rotary body to perform the friction stir welding.
The thickened part of the member can be an integral part of the member, and, e.g., extends to the edge (of the member) which is to be positioned adjacent another member to which the member is to be welded.
Preferably, the protruding portion has a side, furthest from the weld location, which, in cross section, is sloped (e.g., makes an acute angle of less than 90xc2x0 with the plane of the surface of the member (other than the protruding portion); see xcex8 in FIG. 4). Desirably, this side furthest from the weld location makes an angle of 15xc2x0-60xc2x0, preferably 30xc2x0, with the plane of the surface of the member.